[PATCH 16/16] debug_vm_pgtable/ppc64: Add a variant of pfn_pte/pmd

[Aneesh Kumar K.V]

On 8/13/20 11:00 AM, Anshuman Khandual wrote:
> 
> On 08/12/2020 12:03 PM, Aneesh Kumar K.V wrote:
>> The tests do expect _PAGE_PTE bit set by different page table accessors.
>> This is not true for the kernel. Within the kernel, _PAGE_PTE bits are
>> usually set by set_pte_at(). To make the below tests work correctly add test
>> specific pfn_pte/pmd helpers that set _PAGE_PTE bit.
>>
>> pte_t pte = pfn_pte(pfn, prot);
>> WARN_ON(!pte_devmap(pte_mkdevmap(pte)));
>> WARN_ON(!pte_savedwrite(pte_mk_savedwrite(pte_clear_savedwrite(pte))));
>>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com>
>> ---
>>   mm/debug_vm_pgtable.c | 65 +++++++++++++++++++++++++++----------------
>>   1 file changed, 41 insertions(+), 24 deletions(-)
>>
>> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
>> index eea62d5e503b..153c925b5273 100644
>> --- a/mm/debug_vm_pgtable.c
>> +++ b/mm/debug_vm_pgtable.c
>> @@ -31,6 +31,23 @@
>>   #include <asm/pgalloc.h>
>>   #include <asm/tlbflush.h>
>>   
>> +#ifdef CONFIG_PPC_BOOK3S_64
>> +static inline pte_t debug_vm_pfn_pte(unsigned long pfn, pgprot_t pgprot)
>> +{
>> +	pte_t pte = pfn_pte(pfn, pgprot);
>> +	return __pte(pte_val(pte) | _PAGE_PTE);
>> +
>> +}
>> +static inline pmd_t debug_vm_pfn_pmd(unsigned long pfn, pgprot_t pgprot)
>> +{
>> +	pmd_t pmd = pfn_pmd(pfn, pgprot);
>> +	return __pmd(pmd_val(pmd) | _PAGE_PTE);
>> +}
>> +#else
>> +#define debug_vm_pfn_pte(pfn, pgprot) pfn_pte(pfn, pgprot)
>> +#define debug_vm_pfn_pmd(pfn, pgprot) pfn_pmd(pfn, pgprot)
>> +#endif
> 
> Again, no platform specific constructs please. This defeats the whole purpose of
> this test. If __PAGE_PTE is required for the helpers, then pfn_pmd/pte() could
> be modified to accommodate that. We dont see similar issues on other platforms,
> hence could you please explain why ppc64 is different here.
> 

It is not platform specific. set_pte_at is the one that set the 
_PAGE_PTE bit. We don't call that in the test.  The test seems to make 
the assumption that pfn_pte returns a proper pte which is not true.

-aneesh